What Did Scientists Learn After Thousands of Penguins Were Slaughtered by Mountain Lions?

In 2007, only three years after the creation of Monte León National Park along the wild coastline of Argentine Patagonia, efforts to protect penguins took an unexpected turn. A female puma was slaughtering Magellanic penguins in droves. Some of these she would eat, while other surplus kills were left to rot. Before long, her cubs joined in the feast. All told, the family likely killed thousands of penguins over the course of a few nesting seasons.

Conservationists were shocked—what could have happened? Surely these kinds of attacks didn’t occur in the past. The park was created, at least in part, to protect the large penguin colony, which numbers in the tens of thousands. The aquatic birds even feature prominently on the park’s logo.

Wildlife managers stepped in to put a stop to the killing. “They finally decided to sacrifice these animals to protect penguins,” says Javier Ciancio, a marine biologist and ecologist with Argentina’s National Scientific and Technical Research Council.

But new research published in December 2024 in the Journal for Nature Conservation by Ciancio and his colleagues reveals that this kind of predation likely did occur in the past—and it may be why there once weren’t so many penguin colonies on the mainland of South America. That likely changed roughly a century ago, when an influx of sheep farmers led to the extirpation of most land-based predators, and the rise of whaling and the fur trade may have severely reduced marine predators. The long-term ecological consequences of these human interventions may have set the scene for an explosion in mainland penguin populations.

“[Penguins] are occupying a larger area thanks to removing the puma and other predators,” Ciancio says. “That’s the paradox of living in the anthropogenized world.”

In their study, Ciancio and his colleagues examined the importance of penguins in the diet of the four pumas that tore through the colony at Monte León. They also explored the history of this species of penguin.

As Ciancio and his colleagues note in the paper, most seabirds—Magellanic penguins included—only breed in colonies on small offshore islands, or occasionally in rugged cliffsides on the mainland. These kinds of roosts are basically free from land-based predators, which could otherwise make quick work of nests, chicks and even adults, given penguins’ clumsiness on their feet. The Magellanic penguins nest on islands offshore from the mainland coast in South America as well as farther-flung islands like the Falklands. But in the past century or so, they increasingly nest in large colonies on the mainland of South America. Their nesting colonies can be vast, numbering in the hundreds of thousands, usually on relatively flat beaches.

Most Magellanic penguin nest colonies on South America’s mainland are relatively new—especially the really large ones such as those at Punta Tombo and Península Valdés in Argentina. While some evidence exists that penguins at Punta Tombo were in the area in the Miocene Epoch, millions of years ago, the colony there seems to have disappeared until at least 1876, when bird surveys didn’t mention any of the aquatic birds. Dee Boersma, a biologist at the University of Washington, and her colleagues write that penguins likely colonized Punta Tombo in the 1920s. The population remained small until the mid-1940s, when it began to expand rapidly in numbers. Meanwhile, other colonies nearby probably began in the past century or so as well, including the massive one at Península Valdés.

Boersma and her team have been studying the Punta Tombo colony for decades. In a study published in 1990 in the book Penguin Biology, she and her colleagues note that the breeding distribution appears to be moving northward as conditions improved for the species. Colonies around Puerto Madryn such as that at Península Valdés and Punta Tombo now number in the hundreds of thousands.

Ciancio says penguins at Monte León may have thrived for the century leading up to recent decades because of a lack of pumas in the area. Some of the first settlers in coastal Argentine Patagonia were sheep farmers. To better protect their herds, they eradicated all potential predators in the area, including pumas, foxes and smaller endemic wild cats. To extirpate mountain lions from their farms, settlers used a combination of poison, which would have killed not only pumas but other smaller potential predators, and lioneros—experts at hunting down and killing pumas. “We’ve become very effective in eradicating pumas,” Ciancio says.

By removing predators that could have feasted on penguin nests, chicks or even adults, the farmers basically opened up more suitable penguin nesting habitat along the coast, allowing penguins to either expand in population or range, or shift their nesting areas from offshore islands to mainland beaches that may be closer to good forage fish resources.

“The farmer poisoning to kill pumas never would have thought he’d have an effect on the larger marine ecosystem,” Ciancio says. The Patagonian coast of Argentina doesn’t have many offshore islands, places where penguins could nest safe from predators. “Providing the opportunity to breed on the mainland has opened up new habitat.”

The trouble is, for the penguins at least, the arid conditions of coastal Patagonia in Argentina aren’t very good for sheep herding in the long run. Sheep and other types of farming quickly degrade the soil, and high winds in the area then blow away much of what’s left. By the 1990s, many of the shepherds had left the area as a result.

The government moved to protect some of the penguin colonies, creating national parks like Monte León. But this may have been counterproductive, at least for the penguin colonies. The lack of sheep farmers and new protection afforded by national parks meant pumas, foxes and other predators were no longer killed. In some cases, they have returned to coastal areas, where they prey on penguins.

According to stable isotope analysis conducted by Ciancio and his colleagues on the four pumas at Monte León, their diet changed from mostly relying on terrestrial food to one that almost entirely depended on penguins. On top of this, Ciancio notes that pumas, like other cats, often kill many more prey than they can eat. “A puma can kill hundreds of penguins while feeding on only a fraction of them,” he says.

Ciancio adds that pumas could affect penguins in the long term. “Predation is particularly important when the colony is in the early stages of formation,” he says. “This could happen at any time on the continent, but after predation events, penguins may choose to nest elsewhere, in safer locations such as islands.”

Katie Holt, a graduate student in biology at the University of Washington who works with Boersma at Punta Tombo but wasn’t involved in Ciancio’s study, agrees with Ciancio’s finding that when farmers removed the pumas and other big predators, they likely allowed penguins to nest. “Removing predators have now allowed this very charismatic seabird to move in,” she says.

But she doesn’t think that pumas will have a large impact on penguin colonies, even if they come in and kill 100 or so at a time in surplus killing, due to the vastness of these colonies, which can number in the hundreds of thousands.

She also says other factors likely helped the penguins find colonial purchase on the mainland about a century ago. For example, Boersma noted in her 1990 study multiple potential causes for the increasing range of penguins on the mainland in South America, including a decrease in competition for forage fish after the decimation of whales in the early 20th century. Seals and sea lions—predators of penguins and food competitors—were also heavily harvested in the mid-1900s. Indigenous people used to harvest penguins, but they no longer live along much of the coast due to colonial persecution. Climate change over the past century may have changed the productivity pattern of penguin prey as well, making food more abundant for penguins in some areas than it used to be.

Ciancio’s research wasn’t solely focused on the past. His team modeled the way that penguins might affect the population of anchovies off the coast. By using current penguin population numbers to estimate how many forage fish these penguins were likely eating, the team revealed that, in the areas penguins feed, they likely eat more than the fishing fleet captures. “The consumption today is higher than the whole fisheries production,” Ciancio says.

This creates a conservation paradox, Ciancio says, where wildlife managers may need to make tough decisions. “What should we do when human intervention, like the eradication of terrestrial predators, benefits charismatic species like penguins but comes at the expense of less charismatic natural resources, such as forage fish and related marine food webs?” he and his coauthors write in the paper.

While penguins may be eating a lot, Holt isn’t sure the overall effect on forage fish is any different from centuries earlier, when marine mammals like whales, seals or sea lions likely would have taken a larger share. “Before there were many penguins nesting on the coast, there were likely many other top predators feeding on forage fish,” she says.

But difficult questions arise as to how wildlife managers should deal with the situation on the coast. For example, should park managers introduce or welcome pumas into coastal national parks to reduce the impact of penguins on fishing stocks? Or should pumas be taken out to preserve populations of the charismatic birds?

As Ciancio and his colleagues ask in the paper, “Which species hold the most ecological value in these ecosystems?”

This article by Joshua Rapp Learn was first published by The Smithsonian on 13 February 2025. Lead Image: Magellanic penguin colony at Isla Magdalena, Chile. Around 120,000 magellanic penguins (Spheniscus magellanicus) nest in burrows on the island. This medium-sized penguin inhabits the coasts of Chile, Argentina and the Falkland Islands. It reaches an average length of 70 centimetres. The magellanic penguin feeds on fish, cephalopods (such as squid), crustaceans and krill, hunting in groups. Photographed on Isla Magdalena, Chile. Photo by PETER J. RAYMOND / SCIENCE PHOTO LIBRARY.

We create awareness through articles, social media and petitions, bringing wildlife issues to the attention of governments, influential organizations and decision makers.

We support leading wildlife charities through advertising, ad-free subscriptions and your generous donations.

What you can do

Help to save wildlife by donating as little as $1 – It only takes a minute.